Reproduce “ReF-LDM: A Latent Diffusion Model for Reference-based Face Image Restoration” on OpenResearch

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About this paper

Chi-Wei Hsiao, Yu-Lun Liu, Cheng-Kun Yang, Sheng-Po Kuo, Kevin Jou, Chia-Ping Chen

Researchers from MediaTek and National Yang Ming Chiao Tung University developed ReF-LDM, a Latent Diffusion Model for reference-based face image restoration, that leverages a novel CacheKV mechanism to efficiently integrate multiple non-aligned reference images. The model demonstrates superior identity preservation with high Identity Similarity scores and improved computational efficiency, overcoming limitations of prior methods.

Key insights

  • Non-spatially aligned reference features can be efficiently integrated into Latent Diffusion Models by pre-caching Key (K) and Value (V) tokens from a single U-Net pass on reference images, then concatenating these with the KVs computed from the noisy latent in subsequent denoising steps (CacheKV).
  • Applying an identity loss in diffusion models requires careful consideration of noise levels; scaling the loss by sqrt(alpha_t_bar) prevents quality degradation while effectively supervising identity preservation, especially at early, noisy timesteps.
  • Leveraging multiple reference images significantly enhances identity preservation in face restoration, and a mechanism that can implicitly learn correspondences without explicit landmark detection is essential for robustness against severe degradation.

Summary by alphaXiv.

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